The proposed study would use probabilistic models of cellular carcinogenesis, combined with maximum likelihood statistical procedures for estimation of model parameters, to analyze lung cancer mortality among U.S. uranium miners. The parameters used in the models aad estimated from the data would have biological interpretations. They would be used to examine the following issues: 1) the dose-response relationship for radon daughters exposure, particularly as it applies to low level exposures; 2) the nature and extent of interaction between radiation and smoking exposures in respiratory carcinogenesis; 3) the presence or absence of dose rate effect; 4) the effect of age at start of irradiation upon subsequent lung cancer risk; 5) the evolution of risk after termination of exposure. Particular attention will be paid to implications for risk due to occupational radiation exposures at the current standards.